#98170: Lifestyle and Cancer Risk: What We Do (and Do Not) Know

The occasional consumption of certain alcoholic beverages, such as wine, is often promoted by nonmedical resources for cancer prevention. This is uniquely concerning because the consumption of large quantities of alcohol has been definitively linked to an increased risk for certain types of cancer. In fact, in its Report on Carcinogens, the U.S. National Toxicology Program has listed alcoholic beverage consumption as a known human carcinogen since 2000 [5].

According to the Report on Carcinogens, alcohol consumption is most strongly associated with cancer of the mouth, pharynx, larynx, and esophagus; a weaker association exists between alcohol consumption and cancer of the liver and breast. The risk of cancer from alcohol consumption is highest in people who also smoke [5]. Other research has identified an increased risk between moderate to heavy alcohol consumption and colorectal cancer [6].

In general, the available evidence indicates that the more alcohol a person consumes, the higher the risk for a related cancer diagnosis. This research clearly indicates that heavy alcohol consumption carries the highest risk for cancer.

However, research also shows that even those with light-to-moderate alcohol consumption may have a modestly increased risk of certain cancers [7,8]. The World Health Organization (WHO) recently released a statement on this risk, which garnered significant media attention. For the purposes of the statement, light-to-moderate alcohol consumption was defined as less than 1.5 L of wine, 3.5 L of beer, or 0.45 L of spirits per week. The statement refers to data indicating that this level of alcohol consumption was identified as the cause of 23,000 new cancer cases in the European Union in 2017. This represented 13.3% of all alcohol-related cancers [9].

These numbers should be considered in the context of all cancer diagnoses, however. Only 2.3% of all cases of seven alcohol-related cancer types were attributed to light-to-moderate alcohol consumption that year [9]. Additionally, a retrospective review of cancer causes is inherently limited due to the many undocumented factors that can contribute to cancer development. While the researchers were unable to identify other apparent causes of cancer in these individuals—besides alcohol consumption—this does not mean that there were no other contributors to these cancers.

The American Cancer Society recommends that people generally avoid drinking alcohol. For those that do choose to drink alcohol, the organization recommends no more than one drink per day for women and two drinks per day for men. These recommendations assume that one drink is equivalent to 12 ounces of beer, 5 ounces of wine, or 1.5 ounces of hard liquor [10].

Although the evidence supporting a link between alcohol consumption and cancer risk is strong, a recent survey found that more than 50% of adults do not know that alcohol impacts cancer risk. This understanding varied by the type of alcohol consumed, with about 10% of respondents stating that wine decreases cancer risk and about 30% of respondents stating that liquor increases cancer risk [11]. In reality, it is the total quantity of alcohol, not the type of alcohol, that affects cancer risk.

Considering that the strongest evidence evaluating alcohol consumption and cancer risk points to an increased risk for cancer, alcoholic beverages of any type should never be recommended as a preventive measure. Instead, the preventive recommendation should focus on either reducing or eliminating alcohol intake. With multiple studies indicating that alcohol use, and related mortality, has been on the rise in the United States since the COVID-19 pandemic, it may be more important than ever to ensure patients are appropriately informed and counseled on this risk [12].

Artificial sweeteners are commonly vilified as cancer-causing additives that should be removed from the diet. These claims span the gamut of artificial sweeteners, including aspartame, sucralose, saccharin, and acesulfame, although the evidence for each specific sweetener differs.

Many claims of harm stem from small animal studies that have linked these chemicals with an increased risk for cancer, despite the fact that many of these studies used exceptionally high doses of sweeteners, and not all animal studies have yielded these same findings [13]. The majority of the available human research is observational, which makes it difficult to determine causation even in the presence of an apparent association.

One of the largest analyses of this topic to date involved an "umbrella review," or a systematic review of prior systematic reviews and meta-analyses. This umbrella review incorporated only reviews and analyses of research conducted in humans, ultimately finding only weak, non-significant evidence of a link between the use of artificial sweeteners and cancer risk. The correlation remained weak and non-significant for cancer-related mortality as well [14].

Reassure patients—especially those with health issues that warrant the use of artificial sweeteners—that the available evidence does not support removing artificial sweeteners from the diet for the purpose of cancer prevention.

The International Agency for Research on Cancer (IARC) recently labeled aspartame as a possible carcinogen, a decision that resulted in significant news coverage. Importantly, the decision to add this label to aspartame was based on "limited evidence" and did not require an associated change in the previously established acceptable daily intake of aspartame (40 mg/kg) [15].

In response to the IARC decision, the U.S. Food and Drug Administration (FDA) issued a statement clarifying that aspartame's classification as a possible carcinogen does not mean that it is actually linked to cancer. Rather, the FDA ultimately disagreed with the IARC's decision after conducting its own analysis of the existing data, which identified significant shortcomings [16].

Cooked meat is sometimes discussed as a risk factor for certain types of cancer. This concern originated with the discovery that meats cooked at high temperatures over an open flame contain certain types of chemicals (i.e., heterocyclic amines [HCAs] and polycyclic aromatic hydrocarbons [PAHs]) that demonstrate mutagenic properties in laboratory research. In animal research, very high quantities of these chemicals were also found to cause cancer [17].

While some observational research in humans has found a possible correlation between consuming well-done, fried, or barbecued meat and an increased risk for colorectal, pancreatic, or prostate cancer, other observational studies have found no correlation [17].

For people who are concerned about whether they may be exposed to these carcinogens via the meats they eat, some small changes in cooking methods can make a big difference. For example, the risks for exposure to HCAs and PAHs are higher for meats that are cooked at high temperatures for extended durations, and those which are exposed to smoke while cooking. Flipping meat periodically can reduce the quantity of these carcinogens, as can removing charred portions of the meat before eating [17].

Over the years, there has been a growing conversation about the potential for cruciferous vegetables to prevent cancer. The term "cruciferous vegetables" refers to vegetables that fall into the Brassica family, some of the more common of which includes broccoli, cauliflower, cabbage, kale, collard greens, radishes, and turnips.

A group of sulfur-containing chemicals called glucosinolates, which are found in these vegetables, have been the primary driver behind this cancer prevention push. When cruciferous vegetables are prepared, chewed, or broken down in the body, they break down into a number of individual compounds. Two of these compounds (indole-3-carbinol and sulforaphane) have shown anticancer effects in some animal studies. This anticancer activity seems to stem from a number of different mechanisms, including protection against DNA damage, inactivation of carcinogens, and induction of cell death in damaged cells [18].

Unfortunately, as with other dietary interventions, any evidence of benefit in cancer prevention is limited and observational in nature. To date, some smaller cohort studies in Europe and the United States have suggested that increased intake of cruciferous vegetables may be correlated with a modestly reduced risk of certain types of cancers, including colorectal and prostate. However, other cohort studies have not identified a link between cruciferous vegetable intake and cancer risk [18].

There has also been interest in taking dietary supplements that provide sulforaphane and/or indole-3-carbinol. So far, studies of these supplements have been quite small and primarily focused on patients who already have cancer. The benefits of these supplements for reducing overall cancer risk remain unclear.

While there is currently no strong evidence to suggest that a diet high in cruciferous vegetables will reduce a person's risk of cancer, vegetables are an important part of a healthy and well-rounded diet. Patients should always be encouraged to increase their vegetable consumption, cruciferous or otherwise.

At least three pesticides (glyphosate, malathion, and diazinon) are classified by the IARC as probably carcinogenic to humans [19]. Since these pesticides are used on foods which are regularly consumed in the diet, there has been increased interest in opting for organic foods, so as to reduce exposure to pesticides and reduce the risk of associated health issues, such as cancer.

Unfortunately, the evidence is not so straightforward. The rating granted to these three pesticides is primarily based on an association with cancer risk in animal research, whereas human evidence remains limited. Additionally, these ratings pertain to high-volume exposures to these pesticides, such as those that occur in farm workers who are applying the pesticides to crops [19]. This type of exposure differs greatly from exposures obtained from foods which were treated with pesticides (and may or may not have been washed in the interim).

It is unclear whether opting for organic foods will reduce a person's risk for cancer. Observational research on this topic has yielded conflicting findings, with some studies finding no clear association between the consumption of organic foods and cancer risk [20,21,22,23]. As with all observational dietary research, it is difficult to accurately assess a person's organic food intake over time. Additionally, people who choose to consume organic foods may also have other sociodemographic and lifestyle factors that could ultimately alter their cancer risk, confounding any findings.

Organic foods typically come at a significantly increased cost to the consumer. Considering that there is no clear benefit in relation to cancer risk, and that a number of studies indicate that the general nutritional content of organic foods is similar to their non-organic counterparts, there is no adequate evidence to support recommending that patients opt for organic foods.

Over the years, many rumors and myths have made the rounds regarding whether soy can increase a person's risk of cancer. To date, however, research has not validated these concerns. Population research has instead found that soy, as part of the diet or when taken as a supplement, may be protective against breast cancer. This research has consistently found that a high-soy diet in Asian and Asian American women is associated with a reduced risk of breast cancer. However, the amount of soy consumed in a Western diet, even among those who consume the highest amounts of soy, was not found to have a preventative effect [24].

Some early research suggested that soy supplements might stimulate the growth of breast tissue or endometrial cells. However, these findings have not been validated in prospective research.

One clinical study shows that taking a tablet containing 50 mg soy isoflavones daily for 12 months does not alter mammographic or breast MRI tissue density in those at high risk of breast cancer, those with non-endocrine treated breast cancer, or those previously treated for breast cancer and without recurrence [25]. Additionally, a study in adults taking high doses of soy isoflavones, such as 150 mg daily, for five years found no evidence that soy isoflavones increase the risk of atypical endometrial hyperplasia [26,27].

In general, patients should be counselled to follow a healthy diet, which can reduce their risk for a variety of health complications, including, but not limited to, cancer. This healthy diet should generally align with the recommendations found in the U.S. Dietary Guidelines (2020–2025) [35]:

The guidelines clarify that dietary choices should always consider personal preferences, cultural traditions, and budget considerations and should be customized to each individual patient whenever possible [35].

In line with these recommendations, the American Cancer Society specifically recommends that people limit their intake of red and processed meats, sugar-sweetened beverages, and highly processed foods. The organization also emphasizes the importance of consuming nutrient-rich foods, vegetables, fruits, and whole grains [10].

Other dietary components are also periodically suggested for the prevention of cancer. Some of the most common include fiber sources such as oats and barley, as well as "healthy" fats like olive oil and fish oil. While some of these claims are supported (at least in part) by observational research, there is no strong evidence warranting a recommendation to focus on the consumption of these dietary components for cancer reduction. However, these ingredients do provide other health benefits, such as reducing the risk for cardiovascular disease. For this reason, these and other healthy dietary components should be recommended in moderation as part of a healthy diet.

Increased physical activity and exercise is known to reduce the risk for a variety of serious health outcomes and may also reduce the risk for cancer, either directly or indirectly. The Centers for Disease Control and Prevention (CDC) recommends that all adults [36]:

These guidelines provide alternate recommendations for older adults, pregnant adults, and adults with chronic health conditions or disabilities. Additionally, the guidelines focus on the importance of only participating in safe physical activities that are appropriate to a person's current fitness level. Those who are currently inactive and looking to increase their activity levels should "start low and go slow" [36]. The American Cancer Society reiterates these general recommendations for physical activity and also cautions against sedentary behavior, such as sitting or lying down, for extended durations [10].

Observational research has linked higher physical activity with lower cancer risk; however, most of these studies relied on patients reporting their own historical physical activity levels, which can be unreliable. The link between physical activity and reduced cancer risk has been identified in multiple studies for the following forms of cancer: bladder, breast, colon, endometrial, esophageal, kidney, and gastric [37].

While this link is not entirely understood, multiple mechanisms of action have been hypothesized. For example, increased physical activity can result in [37]:

Over the years, it has become increasingly clear that obesity is independently associated with an increased risk of cancer. Obesity is usually identified via body mass index (BMI), an imperfect measure that is calculated using height and weight. Although BMI does not measure body fat directly, it has been moderately correlated with more direct measures of body fat. It is also strongly correlated with specific adverse health outcomes, including development of diabetes, hypertension, heart disease, stroke, and cancer [38].

Classification based on BMI (kg/m²):

The American Cancer Society, in recognition that increased body weight is associated with heightened risk of several types of cancers, recommends that individuals keep weight within the healthy range and avoid weight gain in adult life.

(https://www.cancer.org/cancer/risk-prevention/diet-physical-activity/acs-guidelines-nutrition-physical-activity-cancer-prevention/guidelines.html Last Accessed: May 29, 2025)

Level of Evidence: Expert Opinion/Consensus Statement

The rate of cancers attributed solely to excess body weight between the years 2011 and 2015 were 4.7% for men and 9.6% for women, according to data analyzed from the U.S. Cancer Statistics database. These rates varied by cancer type, with the highest body weight-associated cancer rate occurring with liver and gallbladder cancers, endometrial cancer, and esophageal cancer [39]. A separate study estimated that excess body weight accounted for 4% of all cancers across the world in 2012 [40,41]. The reasons for this correlation are unclear; however, the hypotheses mirror those for physical activity and include elevated levels of sex hormones, insulin, and inflammation [41].

Because obesity is also associated with many other serious health outcomes, such as diabetes and heart disease, all patients should be counseled on weight management. Modest weight loss of 5% to 10% in total body weight has been shown to result in measurable health benefits, including a reduced risk for chronic diseases. Although it is not clear how much weight loss is necessary to reduce a person's risk of cancer, weight loss (and particularly sustained weight loss) at a younger age is anticipated to reduce cancer risk. Research into this topic is currently ongoing, with a focus on people who have undergone bariatric surgery leading to maintained weight loss [41].

Exposure to ultraviolet (UV) light is known to cause early aging of the skin, as well as damage that can ultimately lead to the development of skin cancer. As noted previously, the most commonly diagnosed cancers in the United States are actually skin cancers, albeit nonmalignant ones. These are basal cell carcinoma and squamous cell carcinoma. Melanoma, a less common form of skin cancer, can also be caused by exposure to UV light and represents a greater risk due to its ability to metastasize.

The U.S. Preventive Services Task Force recommends counseling young adults, adolescents, children, and parents of young children about minimizing exposure to UV radiation for persons 6 months to 24 years of age with fair skin types to reduce their risk of skin cancer.

(https://jamanetwork.com/journals/jama/fullarticle/2675556 Last Accessed: May 29, 2025)

Strength of Recommendation: B (There is high certainty that the net benefit is moderate or there is moderate certainty that the net benefit is moderate to substantial.)

Patients should be counseled to avoid unnecessary exposure to UV radiation, which can come from excessive time spent outdoors or via tanning beds. Regardless of age or skin tone, all patients should take steps to protect their skin from sunlight. Some helpful recommendations include [42]:

It can be easy to forget that UV rays can penetrate through windows and clouds and are also reflected off of a variety of surfaces, including water, snow, ice, and sand. This means that even patients who are protected from direct exposure to the sun (for example, via an umbrella while sitting on the beach) may still be subject to reflected UV light. Additionally, patients should be reminded that it is important to reapply sunscreen periodically throughout the day [42].

The FDA provides further advice on selecting a sunscreen product. This advice recommends the use of only broad-spectrum sunscreens, which provide protection against both types of UV light (UVA and UVB) and have been shown to reduce the risk of skin cancer. Additionally, the FDA reminds consumers that all sunscreens will eventually wash off and should not be considered waterproof or sweatproof [43].

Tobacco use is the leading, established cause of cancer and cancer mortality. People who use tobacco products via any method (including smoking and chewing), as well as those who are exposed to tobacco smoke in their environments, are at an increased risk of cancer. Although most people associate smoking with lung cancer, it has actually been shown to increase the risk of many other forms of cancer as well, including cancer of the larynx, mouth, esophagus, throat, bladder, kidney, liver, stomach, pancreas, colon, and cervix [44]. Use of tobacco snuff or chewing tobacco has been shown to increase the risk of mouth, esophagus, and pancreatic cancers [45].

Patients should be counseled to fully avoid the use of tobacco, in any form. Patients who are already using tobacco should be counseled on methods that may be helpful for quitting. There is currently no known safe amount of tobacco use via any method of administration [44]. Similarly, there is no safe amount of secondhand smoke from tobacco. Whenever possible, people should strive to spend their time in a smoke-free environment, and to provide a smoke-free environment to the people around them [46].

The good news is that people who quit smoking will see a slow reversal in their cancer risk levels over time, ultimately reducing their risk of cancer and increasing their life expectancy.

E-cigarettes, also referred to as e-cigs, vaporizers, or vapes, have become popular tobacco alternatives. These products contain pure nicotine (the addictive chemical found in cigarettes) instead of tobacco. When they were first introduced to the market, it was believed that the use of nicotine in place of tobacco would reduce the risk for cancer. However, it is now known that the vapor produced by these products contains other chemicals as well [47].

Due to the relative newness of these products, their long-term impact on cancer risk is not fully understood. Unfortunately, since these products tend to contain a variety of chemicals that have the potential to pose health risks, it is anticipated that long-term health risks may be identified in the future. Additionally, acute health risks have already occurred with these products, including multiple reports of e-cigarette or vaping product use-associated lung injury (EVALI) in 2019 [48]. Recommend caution with the use of e-cigarettes, and ensure that patients are aware of the unknowns.